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High Reproductive Rate (high + reproductive_rate)
Selected AbstractsEarly age reproduction in female savanna elephants (Loxodonta africana) after severe poachingAFRICAN JOURNAL OF ECOLOGY, Issue 2 2009M. J. Owens Abstract A 10-year study revealed that after severe poaching (>93% killed) of elephants (Loxodonta africana) in Zambia's North Luangwa National Park (NLNP) during the 1970s and 1980s, the age of reproduction in females was greatly reduced. Fifty-eight per cent of births were delivered by females aged 8.5,14 years, an age at which elephants were reported to be sexually immature in nearby South Luangwa National Park (SLNP) before poaching. The mean age of females at first birth (AFB) (1993, 1994) was 11.3 years. Prior to poaching, the mean age AFB in SLNP was 16 years. The NLNP age structure and sex ratio were skewed, mean family unit size was reduced, and 37% of family units contained no females older than 15 years. Twenty-eight per cent of family units were comprised entirely of a single mother and her calf, and 8% of units consisted only of orphans who would have been considered sexually immature prior to poaching. Only 6% of survivors were older than 20 years, the age at which females in little-poached populations generally become most reproductively active. After a community-based conservation programme and the UN-CITES ban on the ivory trade were introduced, no elephants were recorded killed. In spite of a high reproductive rate, 6 years after poaching decreased, the density of the NLNP population had not increased, supporting predictions that the removal of older matriarchs from family units will have serious consequences on the recovery of this species. Résumé Une étude qui a duré dix ans a révélé qu'après un braconnage très grave (>93% tués) des éléphants (Loxodonta africana) dans le Parc National de Luangwa Nord (NLNP), en Zambie au cours des années 1970 et 1980, l'âge de la reproduction chez les femelles a fort baissé. Cinquante-huit pour cent des naissances se sont passées chez des femelles qui avaient entre 8,5 et 14 ans, un âge auquel les éléphants étaient dits être encore sexuellement immatures dans le Parc National de Luangwa Sud (SLNP), tout proche, avant le braconnage. L'âge moyen des femelles à la première mise-bas (AFB ,at first birth) (1993, 1994) était de 11,3 ans. Avant le braconnage, l'âge moyen à la première mise-bas était de 16 ans au SLNP. Au NLNP, la structure d'âge et le sex-ratio ont été faussés, la taille moyenne de l'unité familiale a été réduite, et 37% des familles ne contiennent aucune femelle de plus de 15 ans. Vingt-huit pour cent des unités familiales n'étaient composées que d'une mère seule et de son jeune, et huit pour cent n'étaient composées que d'orphelins qui devaient être considérés comme sexuellement immatures avant le braconnage. Seuls six pour cent des survivants avaient plus de 20 ans, l'âge auquel les femelles de populations peu braconnées deviennent généralement les plus actives en matière de reproduction. Après l'introduction d'un programme de conservation communautaire et l'interdiction, par la CITES-UN, du commerce de l'ivoire, on n'a plus enregistré aucun massacre d'éléphant. Malgré un taux élevé de reproduction, la densité de population du NLNP n'a pas augmenté, ce qui conforte les prédictions que l'enlèvement des plus vieilles matriarches des unités familiales aura de sérieuses conséquences sur la restauration de cette espèce. [source] Insights from comparative analyses of aging in birds and mammalsAGING CELL, Issue 2 2010Robert E. Ricklefs Summary Many laboratory models used in aging research are inappropriate for understanding senescence in mammals, including humans, because of fundamental differences in life history, maintenance in artificial environments, and selection for early aging and high reproductive rate. Comparative studies of senescence in birds and mammals reveal a broad range in rates of aging among a variety of taxa with similar physiology and patterns of development. These comparisons suggest that senescence is a shared property of all vertebrates with determinate growth, that the rate of senescence has been modified by evolution in response to the potential life span allowed by extrinsic mortality factors, and that most variation among species in the rate of senescence is independent of commonly ascribed causes of aging, such as oxidative damage. Individuals of potentially long-lived species, particularly birds, appear to maintain high condition to near the end of life. Because most individuals in natural populations of such species die of aging-related causes, these populations likely harbor little genetic variation for mechanisms that could extend life further, or these mechanisms are very costly. This, and the apparent evolutionary conservatism in the rate of increase in mortality with age, suggests that variation in the rate of senescence reflects fundamental changes in organism structure, likely associated with the rate of development, rather than physiological or biochemical processes influenced by a few genes. Understanding these evolved differences between long-lived and short-lived organisms would seem to be an essential foundation for designing therapeutic interventions with respect to human aging and longevity. [source] Contrasting genetic structures of two parasitic nematodes, determined on the basis of neutral microsatellite markers and selected anthelmintic resistance markersMOLECULAR ECOLOGY, Issue 24 2009A. SILVESTRE Abstract For the first time, the neutral genetic relatedness of natural populations of Trichostrongylid nematodes was investigated in relation to polymorphism of the ,-tubulin gene, which is selected for anthelminthic treatments. The aim of the study was to assess the contribution of several evolutionary processes: migration and genetic drift by neutral genetic markers and selection by anthelminthic treatments on the presence of resistance alleles at ,-tubulin. We studied two nematode species (Teladorsagia circumcincta and Haemonchus contortus) common in temperate climatic zones; these species are characterized by contrasting life history traits. We studied 10 isolated populations of goat nematode parasites: no infected adult goat had been exchanged after the herds were established. Beta-tubulin polymorphism was similar in these two species. One and two ,-tubulin alleles from T. circumcincta and H. contortus respectively were shared by several populations. Most of the ,-tubulin alleles were ,private' alleles. No recombination between alleles was detected in BZ-resistant alleles from T. circumcincta and H. contortus. The T. circumcincta populations have not diverged much since their isolation (FST <0.08), whereas H. contortus displayed marked local genetic differentiation (FST ranging from 0.08 to 0.18). These findings suggest that there are severe bottlenecks in the H. contortus populations, possibly because of their reduced abundance during unfavourable periods and their high reproductive rate, which allows the species to persist even after severe population reduction. Overall, the data reported contradict the hypothesis of the origin of ,-tubulin resistance alleles in these populations from a single mutational event, but two other hypotheses (recurrent mutation generating new alleles in isolated populations and the introduction of existing alleles) emerge as equally likely. [source] Modelling the efficacy of entomopathogenic nematodes in the regulation of invertebrate pests in glasshouse cropsJOURNAL OF APPLIED ECOLOGY, Issue 2 2000A. Fenton Summary 1. ,Entomopathogenic nematodes belonging to the families Heterorhabditidae and Steinernematidae are lethal obligate parasites of a wide range of invertebrate species. These nematodes exhibit many characteristics that make them ideal candidates as biological control agents of insect pests (rapid host death, high reproductive rates, easily mass-reared in vitro, easy application techniques). 2. ,However, at present, the number of pest species to which these nematodes are applied successfully is small. Clearly, there is a need to develop existing knowledge of the nematode into a more complete understanding of the nematode,pest system as a whole. 3. ,To consider the potential of entomopathogenic nematodes as biological control agents, we adopted a generalized analytical modelling approach and, using realistic parameter estimates, determined the conditions under which these nematodes can regulate a pest population. 4. ,Stability analyses suggested that entomopathogenic nematodes may not be capable of regulating a host population to a stable equilibrium. Long-term persistence of the host and nematode population is unlikely, due to the highly destabilizing effects of the parasite,host relationship. As such, these nematodes may be better suited to short-term control through inundative application techniques rather than long-term regulation. 5. ,This preliminary generalized model highlights areas where further work is needed. This includes estimation of the probability of nematode infection in the field, the effect of host size on the transmission cycle and the influence of spatial heterogeneity on stability. [source] | ||||||||||